If you are working on a large project, you inevitably end up with a large edmx file if you are doing database first EF work. One tip I like to follow is to export it to a pd file so that I can look at it as a referrence while developing. To do this you firstly need to have a print driver installed that will create PDF files. A good one to chose is PDF Creator from pdfforge, however do a virus scan on this file as my AVG came up with a warning about AdLoad.OpenCandy adware program included in the installation. Once PDF Creator is installed, open up your EDMX file in Visual Studio and go to File > Print Chose PDFCreator as the printer and click the Properties button
Keep it as Portrait if you wish, then press the Advanced button
  Choose ARCH E3 as the Paper Size. This is an architectural size and measures 27 x 39 inches (686 mm× 991 mm)  
  Come back out by clicking the OK buttons until you get to print the document. In the PDF Creator options screen, set the profile to High Quality; it will create a larger file, but will be much clearer when zooming in.  
The simply save it. Happy codeing